ML20042A000

Review of Zion Probabilistic Safety Study Sys Analysis

ML20042A000
Person / Time
Site:	Zion  File:ZionSolutions icon.png
Issue date:	02/15/1982
From:	John Hickman SANDIA NATIONAL LABORATORIES
To:
Shared Package
ML20041G561	List: ML20041G560 ML20042A000
References
ACRS-CT-1420A, NUDOCS 8203220534
Download: ML20042A000 (9)

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PDR ADOCK 05000295 P

PDR P

Introduction This report st=marizes a brief (few days) review of the Zion Probabilistic S3fety Study.(1)

The review was carried.out for The review focuses on comparing the methodoloe.v and the ACRS.

of the analysis which leads to a prediction results of that part of the core melt f recuency with other published or ongoing PRAs.

and consecuence analysis were not reviewed.

Centainment response Tr provide perspective, the methods and results cf this ctudy are (ocene,)(g' FWR power plants:

studies

ntrasted with several NRC,spenscred 2) and IRE?

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.w studies cr, fer that m,a t t e r, any previcus PRAs.

The additien ir

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scope mOst importan* tC this review was the mOre detailed modeling Thus, the mest of external. events, particularly seismic events.

meaningful comparisen with other PRAs is between the nonexternal-event core melt frecuency and the methods and scenaries centribut-ing to it.

This may also be of some sie.nificance in the rec.u.laterv arena, since nonexternal-event core melt calculations,nav. see c.reater use in the r e c. u.1 a t o r v environment in the near term tnan other parts of the PRA in general.

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l NRC PRA Procedures Guide, my impressicn is that this study has I

been carried out bv. ccmpetent people and has made significant methodeloc.ical centributiens to PRA in the area of external events.

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Deepite its manv. thcusand. races, however, the document does net'

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In general, their estimated core melt f recuency does s

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i studies The next section nahes scme cf studies or other current these comparisens.

o Com:arisens with Other Studies Core Melt Frequencies.

For comparison, the estimated core melt freg'uencies from For convenience, I've. arrived at several studies are civen below.

core malt sequence frequencies these by merely summing the dominant medians, or point estimates.

It is be they advertized as neans,means and medians may vary by a factor of two or so.

recogniced that 4.4(104)(mean) rien 3.E(10-0)(mean)

Licn (excluding seismic) 6(10 f)

(median or peint estimate)

S u r r'.

(WASE-1400) e(10 5)

(pcint estimate)

Ocenee ( ?.5 5.'G.? )

- 9(10-0)* (pcint estimate)

ANO ( I ?.I? )

en resu.ts are at the 2

As can ba seen rv :nis comoarison, tne lower end, but net markedly different frem results cf these ether studies.

Dc.inant Accident Initiatcrs (excluding seismic) m is also interesting to compare which initiating, event's either dominating risk er dominatine the core It lead to accidents Fcr purposes of comparing the systems analysis, seismic initiator which was only included in the melt frenuency.

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not appreciably dif ferent from those identified Two noteworthy differences are the absence of core melt are in other studies.

of " Loss of Offsite Power (LOP) transients" from the Zion 'i st and the "trans.. ts without loss of MFW."

The latter does not show up since the main feedwater (MFW) was assumed in the Zion conservative assumption.

The' lower study to be lost, a somewhat of the LOP transient, no doubt, stems from the lower

'icn.

They have never had an LOP and importance frecuency predicted at Thuc, the differences in LOPtve hich reduncancy in the crid system.

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At first glance, this appears to be a larce amount of credit for this complex a series of huran actions.

Apparently, this stems from the fact that the pe=ps will trip off under these conditions, thus will not be damaged and therefere Several factors significant time is available for recovery.

including diagnosis time, the may influence behavior, however,

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As with cther studies, the icn study team turned to event for cataloguing accident sequences.

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ever, their use of event trees and fault trees is scmewhat e.. e. c. -

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As ycu based usuallv.'on a probabilistic argunent.

I in WACH-14CC'with electric b.v the analv.st similar thing was done may recall, a

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s power failure.

My persCnal experience is that when such simpli-j fiCations are made, the models then have limited utility fCr future studies and thus this is not usually the method-of-Choice.

N ev erthele s s, if Competently applied, this metho'd should yield valid results.

Similarly, the fault tree analysis took en an abbreviated.

Character.

As I understand it, the front line systems were redrawn C e p.' "~..'. g ~ h e

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a v most imocr ant Cut sets were then drawn.

The system Cet sets were ceriveC, a.r.ca r e n t a, v..c v..nanC, :Cr eaCr seC.uenCe ref.. e c t i n e.

tne CeoenCenC2es _Cr tnat secuence.

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shCeld v.ield valid results.

Our ex.oerience has been, however, a

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PRA and novel.

1 appears to be a useful CCntributiCn to PRA.

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.o Seismic Analysis I have not delved into the seismic analysis in detail.

I co know that this is pioneering work in PRA.

The question of the acceptability of this methodoloey has been discussed at length within the development effort of the PRA Procedures Guide particu-larly the IEEE/NRC Review Conference on the PRA Procedures Guide.

It was the purpose of that conf erence to bring the PRA co =uniry L".b, C.-

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Ihe human reliability methods appear to fellow NUREG/CR-127E(5) and.1 belie,ve represents the state-of-the-art.

Swain has indicated that most of the estimates of human error probabilities appear to y

.ome except.icns to ts..is are notec

.De re ative y conservative.

3

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Specific Scenarios

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r. "a*.4'.4*v. c' O.64

-v O.95 mav. be rcre appropriate in which case the ATWS,/ core melt secuence cm.

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Zm secenc cue to recircula-credit given fer spray in?ection given a ccre elt

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that 100,000 ca:.lons of water will remain in the Refueline Water.

-..S ) when switch over to recirculation, rom in;ecticn (nr Storage Tan.x 2

anoiner source c water to occurs.

,nis in.'ection water.crov ces insure s.t r a v. c.oeratien anc recuce croca,i,itv. o, containment tne.

failure.

The procedures we have indicate that an injecticn spray pump will be left en until the RWST is emptied and we have found nc for refilling the RWST Tnus, the RWST may

[

LOCA procedural steps

.ce c e.r., e t e c c., water wnen neecec curanc. ccre meat,or'centainnent

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.croba. 3ri.ities anc erha.os tne r i s r..

n c. a i n, inis nas tne entracter s

of.rrevidinc. credit for coerater action bev.end that which is tv.r-ical i

cf PRAs and there#cre nav. deserve further review.

l l

L 9

m

.N-

The third accident sequence, Station Elackout due to a LOP transient, is a dominant contributor to risk.

The calculation is or has been pursued by Buslik, Easterling, and Kolb.

The questions arising have to do with several factors, including the treatment of the increasing trend in the unavailability of the turbine driven the appropriateness of the LOP transient frequency prediction,

pump, and the onsite emergency power restoration assumptions.

Depending of these are treated, the mean for this sequence en the way some..

two orCers o., macnituce hicner tnan tne s t u C V.

COC.C.De 8.0 roaCninC

.O r e C 1 C

• s.

.nis aAsC deserves,crther invest 1C.atlon.

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e. 4. e..\\

. s.. a.... e be ar acequate methodclogy carried cut by competent practitiencrs.

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eee.

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"nh. e e y

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.s sequences, the ATWE/c.cre melt, the LOCA sequence with late melt, and station blackcut, should receive further studv.

Obviousiv, a

' 4. a '. c -.4. 4. c. c..

.h. e a y-c..4 a *. e.n e c e.

c' ' h. e e * " d"; m. e'.k..o d e v.4.'.'

y.

y.

r e c. t a r e a =cre ce t alle c. review inan com.o2etec to date.

believe, hcWever, the interpretation of the data in this 3..

stucv sneu.c ce c a r e : u l., v. considerec..

rcr examrie, hac. tne WASH-l'CC data beunde, used te calculate the V sequence (see c m..

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.+

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~

References a

Commonwealth Edison Company (1)

Zion Probabilistic Safety Study:

of Chicago, 1981 (2)

Reactor Safety Study, WASE-1400 (RUREG-75/014), USNRC, October 1975.

Program, Safety Study Methodology Applicatiens SANDEO-1E97/2, NUREG / CK-16 59.

(3)

Reactor Oconee ?3 PWR Power Flant, Vcl. 2: Kolb, Hatch, May 1981.

Generic Evaluaticn cf Tecdwater Transients and Small Ereak in Westinghouse-designed Operati ng (4)

Los s -o f - Cocia nt Accidents Plants, NUREG-0611, USNRC, January 1950.

Handbook cf Human Reliability Analysis with Emphasis on Nuclear Fower Plant Applications: Swain, Guttman, NUREG/CR-12978, (5)

SANDEO-02OO, March 1960.

(6)

A.

D. Swain, Sandia National Laboratories, perscnal communica-tions.

(7)

Memorandum:

ENL Peer Review of the Zion Probabilistic Safety

Study, A.

J. Euslik te R.

A.

Bari, 1/18/82.

(E)

G.

J. Ke rr, Sandia Naticnal Laberater es, perscnal ecmmunica-tiCr.

l.

l t

1 i

i

.